High-surface area functional material coated structures

ABSTRACT

Methods for forming an interconnected network of solid material and pores, with metal residing only at the air/solid interface of the interconnected network structure are described. In certain embodiments, nanoparticle decorated sacrificial particles can be used as sacrificial templates for the formation of a porous structure having an interconnected network of solid material and interconnected network of pores. The nanoparticles reside predominantly at the air/solid interface and allow further growth and accessibility of the nanoparticles at defined positions of the interconnected structure. SEM and TEM measurements reveal the formation of 3D interconnected porous structures with nanoparticles residing predominantly at the air/solid interface of the interconnected structure.

This invention was made with government support underFA9550-09-1-0669-DOD35CAP awarded by the U. S. Air Force. The governmenthas certain rights in the invention.

COPYRIGHT NOTICE

This patent disclosure may contain material that is subject to copyrightprotection. The copyright owner has no objection to the facsimilereproduction by anyone of the patent document or the patent disclosureas it appears in the U.S. Patent and Trademark Office patent file orrecords, but otherwise reserves any and all copyright rights.

CROSS-REFERENCES TO RELATED APPLICATIONS

This patent application claims the benefit of the earlier filing date ofInternational Patent Application No. PCT/US2014/044939, filed on Jun.30, 2014, which claims the benefit of U.S. Patent Application No.61/840,991, filed on Jun. 28, 2013, the contents of which areincorporated by reference herein in its entirety.

INCORPORATION BY REFERENCE

All patents, patent applications and publications cited herein arehereby incorporated by reference in their entirety in order to morefully describe the state of the art as known to those skilled therein asof the date of the invention described herein.

FIELD OF THE INVENTION

The present application relates to high surface area structures coatedwith functional material. More particularly, the present applicationrelates to high surface area structures coated with functional materialsthat may be useful in applications, such as catalytic, optical,antibacterial, sensing and the like applications.

BACKGROUND

Many different applications employ the use of functional material.Generally, this functional material needs to contact the material ofinterest (e.g., reactants, analytes, etc.) to be active. Particularly,if a solid support was desired, the functional materials were added tothe solid support, but many remained inaccessible due to the fact thatmost were embedded into the solid support material fully encasing thefunctional material or were not in an active enough state due to otherreasons (agglomeration, change in chemical state, or both).

SUMMARY

In certain embodiments, the present disclosure is directed to a methodfor fabricating a porous structure. The method includes attaching of oneor more nanometer sized functional material to the surface ofsacrificial particles to obtain nanomaterial-modified sacrificialparticles, wherein said plurality of nanometer sized functional materialhave a size that is less than 7.75% of the characteristic size of thesacrificial particles; arranging the nanomaterial-modified sacrificialparticles into an assembly containing an arrangement ofnanomaterial-modified sacrificial particles having an interconnectedinterstitial space of pores between said nanomaterial-modifiedsacrificial particles; filling the assembly with a material that fillsthe interconnected interstitial space of pores; and removing thesacrificial particles to form an interconnected porous network structurecomprising an interconnected network of solid material defining aninterconnected network of pores; wherein the one or more nanometer sizedfunctional material reside predominantly on the surfaces of theinterconnected network of solid material defining an interconnectednetwork of pores.

In certain embodiments, the sacrificial particles include colloidalparticles.

In certain embodiments, the interconnected porous network structure hasa porosity that is greater than 50%.

In certain embodiments, the one or more nanometer sized functionalmaterial are selected from the group consisting gold, palladium,platinum, silver, copper, rhodium, ruthenium, rhenium, osmium, iridium,iron, cobalt, nickel and combinations thereof.

In certain embodiments, the one or more nanometer sized functionalmaterial are selected from the group consisting of silicon, germanium,tin, silicon doped with group III or V elements, germanium doped withgroup III or V elements, tin doped with group III or V elements, andcombinations thereof.

In certain embodiments, the one or more nanometer sized functionalmaterial are selected from the group consisting of beryllia, silica,alumina, noble metal oxides, platinum group metal oxides, titania,zirconia, hafnia, molybdenum oxides, tungsten oxides, rhenium oxides,tantalum oxide, niobium oxide, vanadium oxides, chromium oxides,scandium, yttrium, lanthanum and rare earth oxides, thorium, uraniumoxides and combinations thereof.

In certain embodiments, the one or more nanometer sized functionalmaterial comprise mixed metal oxides (HMOs), containing alkaline,alkaline earth, rare earth and noble and other metals, heteropolyacidsor combinations thereof.

In certain embodiments, the one or more nanometer sized functionalmaterial are selected from the group consisting of pure and mixed metalsulfides, other chalcogenides, nitrides, other pnictides and mixturesthereof.

In certain embodiments, the one or more nanometer sized functionalmaterial include catalysts for chemical reactions.

In certain embodiments, the interconnected network of solid material isa crystalline inverse opal structure.

In certain embodiments, the interconnected network of solid material isa disordered interconnected structure.

In certain embodiments, the solid material is selected from the groupconsisting of alumina, silica, titania, inorganic sol-gel derivedoxides, polymers, random copolymers, block copolymers, dendriticpolymers, supramolecular polymers, metals and combinations thereof.

In certain embodiments, the sacrificial particles are selected from thegroup consisting of polystyrene (PS) colloidal particles, silicaparticles, acrylate particles, alkylacrylate particles, substitutedalkylacrylate particles, poly(divinylbenzene) particles, polymers,random copolymers, block copolymers, dendritic polymers, supramolecularpolymers, and combinations thereof.

In certain embodiments, the method further includes: providing a growthsolution to form a continuous shell residing predominantly at theinterface between said network of solid material and said network ofpores.

In certain embodiments, the method further includes: providing a growthsolution to grow said one or more nanometer sized functional materialattached to the surface of sacrificial particles.

In certain embodiments, the growth of the one or more nanometer sizedfunctional material forms a nanoshell.

In certain embodiments, the arranging and the filling are carried outsimultaneously.

In certain embodiments, the arranging and the filling are carried outusing emulsion templating.

In certain embodiments, the method further includes: providingadditional functional material to the one or more nanometer sizedfunctional material that reside predominantly at the interface betweensaid interconnected network of solid material and said interconnectednetwork of pores.

In certain embodiments, the present disclosure is directed to aninterconnected porous network structure that includes an interconnectednetwork of solid material defining an interconnected network of pores,wherein the interconnected solid material has a crystalline inverse opalstructure; and nanoparticles residing predominantly on the surfaces ofsaid interconnected network of solid material defining an interconnectednetwork of pores.

In certain embodiments, the nanoparticles are selected from the groupconsisting of metal nanoparticles, semiconductor nanoparticles, metaloxide nanoparticles, mixed metal oxide nanoparticles, metal sulfidenanoparticles, metal chalcogenide nanoparticles, metal nitridenanoparticles, metal pnictide nanoparticles and combinations thereof.

In certain embodiments, the nanoparticles are selected from the groupconsisting of gold, palladium, platinum, silver, copper, rhodium,ruthenium, rhenium, osmium, iridium, iron, cobalt, nickel andcombinations thereof.

In certain embodiments, the nanoparticles are selected from the groupconsisting of silicon, germanium, tin, silicon doped with group III or Velements, germanium doped with group III or V elements, tin doped withgroup III or V elements, and combinations thereof.

In certain embodiments, the nanoparticles include catalysts for chemicalreactions.

In certain embodiments, the nanoparticles are selected from the groupconsisting of silica, alumina, beryllia, noble metal oxides, platinumgroup metal oxides, titania, zirconia, hafnia, molybdenum oxides,tungsten oxides, rhenium oxides, tantalum oxide, niobium oxide, chromiumoxides, scandium, yttrium, lanthanum, ceria, and rare earth oxides,thorium and uranium oxides and combinations thereof.

In certain embodiments, the solid material is selected from the groupconsisting of silica, titania, alumina, zirconia, hafnia, inorganicsol-gel derived oxides, polymers, random copolymers, block copolymers,branched polymers, star polymers, dendritic polymers, supramolecularpolymers, metals and combinations thereof.

In certain embodiments, the nanoparticles are grown in size up to andincluding to form a continuous shell residing predominantly at theinterface between said network of solid material and said network ofpores.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages will be apparent upon consideration of thefollowing detailed description, taken in conjunction with theaccompanying drawings, in which like reference characters refer to likeparts throughout, and in which:

FIG. 1 is a schematic illustration showing a method for forminginterconnected porous network structure having nanoparticles residingonly at the air/solid interface in accordance with certain embodiments;and

FIG. 2A-2C is an example of using a spherical colloidal particle assacrificial particle and using co-assembly method to form aninterconnected porous network structure having nanoparticles residingonly at the air/solid interface in accordance with certain embodiments;and

FIG. 3A-3C shows images of colloidal particles decorated with differentsized metal nanoparticles in accordance with certain embodiments;

FIG. 4A-4I demonstrates the varying degree of long range ordering thatcan be obtained depending on the size of nanoparticles in accordancewith certain embodiments;

FIG. 5A-5C shows the growth of metal nanoparticles that reside at theair/solid interface of the interconnected porous structure in accordancewith certain embodiments; and

FIG. 6A-6B is a schematic illustration showing a method to formhierarchical interconnected porous network structure having twodifferent nanoparticles residing only at the air/solid interface inaccordance with certain embodiments.

DETAILED DESCRIPTION

The three dimensional (3D) interconnected porous structures, synthesizedfrom a sacrificial template assembly, provide a high degree ofinterconnected pores having a high surface area with well-defined poresize and accessibility of a porous network. Such structures arepotential candidates for applications in sensing and catalysis. Theincorporation of functional nanoparticles into interconnected porousstructure can introduce certain desired properties, such as optical,sensing and catalytic properties. Typically, such particles areincorporated by the infiltration of the preformed porous network withthe solution containing nanoparticles (e.g., metal particles) or by athree-phase co-assembly deposition, simultaneously assembling polymercolloids, a matrix material (e.g. silica) and nanoparticles. In theformer, low surface density and poor interface adhesion of nanoparticlesis observed; in the latter, many of the nanoparticles remain completelyembedded within the matrix material and a high degree of loading wasneeded to provide access to the nanoparticles so that some smallfraction of the metal nanoparticles can sit at the air/solid interface.

The present application provides a precise control over nanoparticlesdistribution onto the surfaces of a network of interconnected solidmaterial defining an interconnected network of pores, such as, forexample, inverse opals structures. In particular, metal nanoparticlescan be placed at the air/solid interface of the network ofinterconnected solid material defining an interconnected network ofpores, resulting in a higher accessibility of nanoparticles andenormously enhancing their effective utilization as catalysts, sensors,and surface-enhanced Raman spectroscopy (SERS) substrates.

As used herein, an “interconnected structure” refers to a structure thathas at least two different continuous phases. An “interconnected porousnetwork structure” refers to a structure that has at least onecontinuous pore phase and at least one continuous solid material phase.

In certain embodiments, the interconnected porous network structure hasa porosity that is greater than 70 vol % approaching cubic closed packedstructures (e.g., 74%). In certain embodiments, the interconnectedporous network structure has a porosity that is greater than 50 or 53vol % as in cubic or hexagonal or random structures. In certainembodiments, the porosity is greater than 80% or more than 90% (e.g., byutilizing mesoporous silica that provides even greater porosity withinthe solid material). In certain embodiments, the interconnected porousnetwork structure has a well-defined pore size that varies less than 5%with respect to the pore diameters.

FIG. 1 shows a schematic illustration for placing nanoparticlespredominantly on the surface of the continuous solid (i.e.,predominantly at the air-solid interface of an interconnected porousnetwork structure). As shown in FIG. 1, sacrificial particles can beprovided, where they may already have or can be optionally provided withfunctional groups that can adhere to nanoparticles. As shown, thesacrificial particle can be any shape, such as spherical or random.Other shapes of the sacrificial particles will be readily apparent toone skilled in the art.

FIG. 2A shows one particular example where spherical colloidal particles(e.g. polystyrene “PS”) bearing functional groups that can adhere tonanoparticles can be formed. The schematic in FIG. 2A provides oneillustrative example where the PS surfaces are functionalized withcarboxylic groups, followed by their modification with2-aminoethanethiol to introduce thiol functionalities to the colloidsurface.

Subsequently, as shown in FIG. 1, the nanoparticles can be attached tothe surfaces of the sacrificial particles. In certain embodiments, thesacrificial particles can be modified on their surfaces with one or morefunctional materials using various binding mechanisms depending on thetype of material to be attached, such as covalent attachment (e.g.,metal nanoparticle attachment through thiol chemistry), dative bonding(e.g., complexation with a wide range of inorganic or organic ligands orvia organometallic moieties) or electrostatic attraction betweenopposite-charged colloids and nanoparticles. FIG. 2A shows a particularexample where polystyrene (PS) colloidal particle is used as thesacrificial particle and gold nanoparticles are covalently attached tothe colloidal surface (e.g., PS) through the functional groups (e.g.,thiol moiety).

FIG. 2B shows one exemplary polystyrene (PS) colloidal particle that hasnanoparticles attached thereon through Au—S covalent bonding. In FIG.2B, the gold nanoparticles have an average diameter of about 12 nm andthe PS colloidal particles have an average diameter of about 480 nm.

While the specific examples in FIGS. 2A and 2B are described in terms ofPS colloidal particles and gold nanoparticles, numerous other types ofmaterials can be utilized. For example, in certain embodiments, silicaparticles, poly methyl methacrylate particles (PMMA), other acrylate,alkylacrylate, substituted alkylacrylate, crosslinked PS or PMMAparticles or poly(divinylbenzene) particles can be utilized as thesacrificial particles. Other polymers of different architectures, randomand block copolymers, branched, star and dendritic polymers,supramolecular polymers, and the like can be utilized as the sacrificialparticles. Sizes of these sacrificial particles may range from about 50nm to about several tens or hundreds of microns. Some exemplary sizesinclude 100 nm to about 1000 nm to provide either specific opticalproperties or improved assembly characteristics that are not largelyaffected by gravity. In certain embodiments, the size may range fromabout 100 nm to about 500 nm. As will be apparent to one of skill in theart, other sacrificial particles can also be utilized.

In certain embodiments, the nanoparticles can include metal (e.g., gold,silver, platinum, palladium, ruthenium, rhodium, cobalt, iron, nickel,osmium, iridium, rhenium, copper, chromium, bimetals, metal alloys, andthe like and combinations thereof) nanoparticles, semiconductor (e.g.,silicon, germanium, and the like, pure or doped with elements orcompounds of group III or V elements, and combinations thereof)nanoparticles, metal oxide (e.g., V₂O₅, silica, alumina, noble metaloxides, platinum group metal oxides, titania, zirconia, hafnia,molybdenum oxides, tungsten oxides, rhenium oxides, tantalum oxide,niobium oxide, chromium oxides, scandium, yttrium, lanthanum and rareearth oxides, thorium and uranium oxides and the like) nanoparticles,metal sulfide nanoparticles, or combinations thereof.

In certain embodiments, selection of the desired nanoparticles can bebased on providing certain desired properties. For example, Pd or Pt,other noble metal or metal oxide particles can provide catalyticproperties, while Ag, copper or oxide (e.g., V₂O₅) nanoparticles canprovide antibacterial properties. Other nanoparticles, such assemiconductor nanoparticles for semiconducting properties, magneticnanoparticles for magnetic properties, and/or quantum dots for opticalproperties, can be utilized as desired.

In certain embodiments, more than one different type of nanoparticlescan be provided onto the colloidal particles. For instance, both Pd andPt (or any other binary, tertiary or higher order desired combination ofcatalytically active metals) nanoparticles can be provided to providedifferent catalytic properties to different reactants. Such nanomaterialmodified colloidal particles can be formed by reacting the colloidalparticles with a mixture of first (e.g., Pd) and second (e.g., Pt), aswell as any additional nanoparticles or their precursors. Alternatively,such nanomaterial modified colloidal particles can be formed bysequentially reacting colloidal particles with a first type ofnanoparticles or their precursors followed reaction with a second typeof nanoparticles or their precursors. Many different ways to providesuch multiple functionality would be readily evident to one skilled inthe art.

In certain embodiments, as shown in FIG. 1, the amount and/or size ofthe nanoparticles can be optionally further increased after attachmentto the sacrificial particles. In certain embodiments, the nanoparticlescan be grown further in size through the addition of a growth solution.In certain embodiments, the growth solution can be provided so that ashell (or nearly complete shell) forms around the sacrificial particles.For example, FIG. 3 shows TEM images of gold nanoparticle decorated PScolloidal particles having an average diameter of about 480 nm. In theseillustrative examples, after decorating the PS colloids with small goldnanoparticles (np) having diameter of ˜2 nm using the same methoddescribed on FIG. 2A, the size of the gold nanoparticles were increasedby introducing the gold nanoparticle growth solution. FIG. 3A shows thegold nanoparticles are about 2 nm in diameter. When growth solution isapplied after attachment to the colloidal particle, the diameter of thegold nanoparticles increases gradually, as shown in FIGS. 3B and 3C,also resulting in a more densely covered surface or a shell on thesurface.

In certain embodiments, as shown in FIG. 1, additional functionality canbe provided to the nanoparticle-modified sacrificial particles asdesired. For example, it may be desirable to improve the stability ofthe nanoparticle-modified sacrificial particles in suspension and/orwith the final backfilled material (as will be described in greaterdetail below) or to introduce additional functionality. For example, thenanoparticle-modified sacrificial particles can be coated with amaterial that is more compatible with the final backfilledinterconnected solid material. Specific examples include coating thenanoparticles with silica if the final backfilled interconnected solidmaterial will be titania or alumina. Another specific example includescoating the nanoparticles with titania or alumina if the backfilledinterconnected solid material is formed using a silica sol-gelchemistry. Yet another specific example includes providing chemicalfunctionalization to provide silane groups on the nanoparticles topromote condensation with metal oxide sol-gel chemistries. Numerousother examples will be readily apparent to one skilled in the art.

In certain embodiments, although many differently sized nanoparticlescan be utilized, such as 1 nm to several tens of nm, the nanoparticlesand/or the shell that forms around the sacrificial particles are lessthan about 7.75% of the characteristic size (e.g., diameter, longestdimension, shortest dimension, etc.) of the sacrificial particle. Forexample, the nanoparticles and/or the shell that forms around thesacrificial particles are less than 31 nm in the case of sacrificialparticles of the size of 400 nm as shown in the Figures. In certainembodiments, the nanoparticles and/or the shell that forms around thesacrificial particles are less than 5%, 2%, or 1% of the sacrificialparticle diameter. In certain embodiments, the nanoparticles and/or theshell that forms around the sacrificial particles are less than 100, 40,20, 15 or 10 nm. In certain embodiments, the nanoparticles and/or theshell that forms around the sacrificial particles are less than about 20nm, less than about 15 nm, or less than about 10 nm. In certainembodiments, the nanoparticles and/or the shell that forms around thesacrificial particles are less than about 5 nm or less than about 2 nmor less than about 1 nm in size. In certain embodiments, thenanoparticles and/or the shell that forms around the sacrificialparticles are between about 1 nm to about 100 nm. In certainembodiments, nanoparticles that form around the sacrificial particlesare less than 15 nm. In certain embodiments, the shell that forms aroundthe sacricifical particles have a thickness that is smaller than 20, 15,or 10 nm. Generally, whether nanoparticles or a shell is attached to thesacrificial particles, these structures will be referred to as“nanomaterial modified sacrificial particles.”

Then, as shown in FIG. 1, the nanomaterial modified sacrificialparticles can be utilized for the formation of an assembly, such as anopal structure. In certain embodiments, the nanomaterial modifiedsacrificial particles can be arranged into a desired assembly having aninterconnected interstitial space of pores between the nanomaterialmodified sacrificial particles. In certain embodiments, such an assemblymay have a crystalline structure (e.g., opal structure), glassystructure (e.g., glass-like short range order) or be completelydisordered (e.g., no short or long range order).

The schematic in FIG. 2C provides one illustrative example of using agold modified PS colloids using a two phase self-assembly process in thepresence of the silica precursor Si(OEt)₄. However, many differenttechniques to provide an assembly can be utilized, such as self assemblyof composite colloids from solution, drop casting, spin coating,microfluidic device, emulsion templating, spray coating, spray drying,induced aggregation in solution or engineering techniques as grinding ormilling of preformed powder, infiltration of sol-gel material or atomiclayer deposition (ALD).

Thereafter, as shown in FIG. 1, such an assembly can be then backfilledwith a material that can backfill the interstitial spaces between thenanomaterial modified sacrificial particles. In other embodiments, theassembly can be formed in conjunction with a material that can backfillthe interstitial spaces between the nanomaterial modified sacrificialparticles, as in so-called co-assembly method shown in FIG. 2C. FIG. 2Cagain shows a particular example, where the nanoparticles-modifiedsacrificial colloids assemble into an opal structure in the presence ofthe matrix material (e.g., sol-gel solution of a metal oxide or silica)that fills interstitial spaces between the nanoparticle-modifiedcolloidal nanoparticles to form an inverse opal structure after theremoval of the sacrificial particles by heat treatment.

As shown in FIG. 1, the sacrificial particles can be removed leaving aninterconnected porous network structure having nanoparticlespreferentially located at the air/network interface. FIG. 2C providesone illustrative example where the formation of the opal structure andbackfilling described above is followed by calcination at 500° C. toproduce inverse opals with gold nanoparticles present predominantly atthe interface of the interconnected solid material and theinterconnected pores (i.e., the region where the colloidal particlesused to be). However, depending on the type of sacrificial particles andthe solid material to be formed for the interconnected porous networkstructure, many different temperatures can be utilized. For example, ifa polystyrene is used as the sacrificial material and silica is used asthe interconnected solid network structure, use of a temperature thatexceeds the temperature of complete decomposition of the sacrificialparticles (e.g., 400° C.) but below the decomposition temperature of thesolid matrix material (SiO₂) temperature may be carried out. In thiscase, the temperature to remove the sacrificial particles may, forexample, be 500° C.

There is no limitation on the type of solid materials that can beutilized for the interconnected porous network structure. In certainembodiments, the interconnected porous network structure can includesilica, titania, alumina, zirconia, other oxides (e.g., inorganicsol-gel derived oxides, mixed oxides), polymers of differentarchitectures, random and block copolymers, branched, star and dendriticpolymers, supramolecular polymers, metals and combinations thereof. Forinstance, combination of silica precursor with polymer to producemesoporous silica matrix with enhanced porosity. In certain embodiments,precursors that react, solidify or polymerize to form the solid materialcan be utilized. Other techniques that will be readily apparent to oneskilled in the art, such as electroplating, can be utilized as well.

In certain embodiments, selection of the material for the interconnectednetwork structure can be based on any desired properties. For example,use of titania or zirconia can provide certain desired photocatalyticand/or electrical properties. The use of polymers as matrix material mayresult in soft and dynamic network structures.

While not wishing to be bound by theory, the presence of nanoparticles(e.g., gold metal nanoparticles) or nanoshell (e.g., gold shell that wasgrown after gold metal nanoparticle attachment) on the surfaces of thesacrificial particles (e.g., polystyrene) are expected to preventformation of an interconnected structure between the sacrificialparticles (e.g., polystyrene portions do not touch each other). In thiscase, one skilled in the art would not have expected to be able toremove the sacrificial particles in the presence of the backfilledmaterial as there is a lack of an interconnected pathway between thesacrificial particles to allow sufficient removal of the sacrificialparticles. Nevertheless, it has been unexpectedly found that byutilizing sufficiently small nanoparticles or nanoshells, despite thefact that the sacrificial particles themselves may not be touching eachother, removal of the sacrificial particles was possible and resulted ininterconnected pores.

Moreover, another unexpected result is that when the sacrificialparticles are being removed, the nanoparticles or the nanoshell (ifgrown) are able to transfer themselves onto the solid material withoutbeing removed along with the sacrificial particles so that they remainpredominantly on the surface of the interconnected solid material (i.e.,at the interface between the interconnected solid material and theinterconnected pores). Furthermore, the nanoparticles do not agglomeratewith each other during this removal step of the sacrificial particlesand generally remain well distributed throughout the interconnectedporous network structure.

Moreover, FIG. 4 shows the formation of an ordered inverse opalinterconnected porous network structure using various composite PScolloids shown in FIGS. 2B and 3A-3C. FIGS. 4A through 4C show anordered inverse opal structure when PS colloids modified with smallAuNPs (Au seeds) of less than 5 nm in diameter have been used (see FIG.3A). The crystalline order of the inverse opal is visible by thepresence of Moiré fringes (these are the lines one can see) thatindicate periodic arrangements of the individual colloids that are toosmall to be resolved in the image. In certain embodiments, a long rangeordered inverse opal structures, with reduced number of defects ishighly desirable. For example, long range ordered inverse opal structureprovides well-ordered structures that span at least 100 microns, atleast 1 mm, or even at least 1 cm, without significant amount ofdefects, such as cracks and the like. Without wishing to be bound bytheory, there may be certain processing parameters that allow theformation of long-range ordered inverse opal structures while otherconditions lead to structures having a greater degree of defects and/ordisorder. For instance, long range ordered inverse opal structures maybe obtained by utilizing PS colloidal particles that have been modifiedwith small metal nanoparticles, such as nanoparticles less than 5 nm,less than 3 nm, or even less than 2 nm in diameter.

In contrast, using larger nanomaterial modified colloidal particlesleads to less ordered structures. FIG. 4D-F shows the formation of aninterconnected porous network structure using PS colloids modified withnanoparticles depicted on FIG. 3B having a size of about 450 nm. FIG.4G-I shows inverse opal structures made using PS colloids modified withgold nanoparticles having ˜12 nm in diameter. Furthermore, theadditional growth of gold shell around the PS colloid (as shown in FIG.3C) resulted in the less stable colloidal dispersion giving rise tocolloidal precipitation after ˜3-4 h.

Nevertheless, despite the reduced order, differently sized nanoparticles(or different amounts of the functional material) can form aninterconnected porous network structure having a precise placement ofthe functional material at the interface of solid material and the pore.

In certain embodiments, the amount of functional material present at theair/network interface can be further increased after the formation of aninterconnected porous network structure. As shown in FIG. 3, ananoparticle growth solution can be introduced through theinterconnected pores of the interconnected porous network structure,thereby forming a shell of the desired functional material. Theillustrative example shown in FIG. 5 introduced a AuOH/CH₂O solutioninto an inverse opal structure having gold nanoparticles at theair/inverse opal interface to form a gold shell at the air/inverse opalinterface.

FIG. 5A shows an SEM image of inverse opals made from gold seed-modifiedPS colloids. FIG. 5B shows an SEM image of the same sample after 12 himmersion in a gold salt solution. Similarly, FIG. 5C shows an SEM imageof the same sample after 48 h immersion in a gold salt solution. Asshown, the presence of the gold at air/solid interface increases overtime, as evidenced by the higher signal arising from the higher electrondensity of gold especially in backscattered electron imaging (imageslabeled ESB).

The current approaches described herein provide superior benefits overprevious approaches. The precise placement of functional material atair/matrix interface increases their accessibility for desired reactions(e.g. catalysis) and makes the resulted composite porous structureshighly efficient using high degree of morphological control. Forexample, the high number of metal nanoparticles present at the air/solidinterface may allow one to formulate a relatively uniform shell aroundthe air/solid interface.

Accordingly, the present disclosure provides a synthetic approach toobtain precise confinement of nanoparticles on interfaces ofinterconnected porous network structures, such as inverse opal structuresurface, that have short or long range ordering. In certain embodiments,the network structure may even be a disordered structure. Such astructure allows the formation of highly efficient porous functionalmaterials with controlled reactivity, in addition to the tailoring ofthe network structure's optical properties through the presence of anabsorbing component. In addition, the accessibility of goldnanoparticles at the air/network interface permits further growth ofnanoparticles at defined positions of the inverse opal structure. Thismethod provides a high level of synthetic flexibility and permitsremarkable control over the structural parameters of composite particlesleading to the formation of novel types of “heterocomposite”(multicomposite) inverse opal structures with well-defined morphology,composition and structure-property relationships.

The potential use of such hybrid, porous network structures with surfaceaccessible functional nanoparticles may extend into various applicationsincluding optics (photonic crystals), heterogeneous catalysis andbio-catalysis, sensing, surface enhanced Raman scattering applications,photocatalysis, electrode materials, enhancement of solar cellperformance and others.

Many different modifications are within the skill of one skilled in theart. In certain embodiments, once the interconnected porous networkstructure having the desired nanoparticles or nanoshells located at theair/network structure interface is formed, further modification can becarried out to provide desired properties, such as molecular complexesfor catalysis, stimuli responsive molecules for sensing, and the like.Desired functional groups that provide desired functionalities can beprovided thereon.

In other embodiments, the interconnected porous network structuresdescribed herein can be formed in a variety of different shapes,depending on desired applications. For example, the structures can beformed in the form of films, shards (e.g., flakes, debris), sphericalassemblies and powders.

In certain embodiments, the degree of porosity can be increased. Incertain embodiments, binary or higher order mixtures of particles can beutilized. In certain embodiments, mesoporous materials can be utilizedas the matrix materials.

In some other embodiments, as shown in FIG. 6, hierarchical materialscan be prepared by creating superstructures of the interconnected porousnetwork structure with dimensions in the micrometer range. As anexample, FIG. 6A shows emulsion templating of a nanomaterial modifiedcolloidal dispersion in the presence of the backfilling material can beused to create spherical superstructures of the interconnected porousnetwork structure. In certain embodiments, superstructures can be formedthat contain different types of nanoparticles (e.g., “PS@A” and “PS@B”).Then, these micron scale superstructure units can be further assembledinto a crystal or a disordered arrangement, either using one type ormultiple types of superstructures having different nanoparticles. Forexample, as shown in FIG. 6B, multicomponent systems can be created thathave different functional nanoparticles at different places ofarchitecture. This can allow multiple catalytic processes within oneunit. Moreover, as a result, a hierarchical, porous material resultsthat has voids over multiple length scales, ranging from the initialpores to the voids arising from the assembly of the micron-scale porouselements which may allow better diffusion or better flow of liquids(i.e. less clogging).

Upon review of the description and embodiments provided herein, thoseskilled in the art will understand that modifications and equivalentsubstitutions may be performed in carrying out the invention withoutdeparting from the essence of the invention. Thus, the invention is notmeant to be limiting by the embodiments described explicitly above.

What is claimed is:
 1. An interconnected porous network structurecomprising: an interconnected network of solid material defining aninterconnected network of pores, wherein the interconnected solidmaterial has an inverse opal structure; and nanoparticles residing atdefined positions of an interface between the network of pores and saidinterconnected network of solid material defining the interconnectednetwork of pores.
 2. The interconnected porous network structure ofclaim 1, wherein said nanoparticles are selected form the groupconsisting of metal nanoparticles, semiconductor nanoparticles, metaloxide nanoparticles, mixed metal oxide nanoparticles, metal sulfidenanoparticles, metal chalcogenide nanoparticles, metal nitridenanoparticles, metal pnictide nanoparticles and combinations thereof. 3.The interconnected porous network structure of claim 1, wherein saidnanoparticles are selected from the group consisting of gold, palladium,platinum, silver, copper, rhodium, ruthenium, rhenium, osmium, iridium,iron, cobalt, nickel, bimetals, metal alloys, and combinations thereof.4. The interconnected porous network structure of claim 1, wherein saidnanoparticles are selected from the group consisting of silicon,germanium, tin, silicon doped with group III or V elements, germaniumdoped with group III or V elements, tin doped with group III or Velements, and combinations thereof.
 5. The interconnected porous networkstructure of claim 1, wherein said nanoparticles comprise catalysts forchemical reactions.
 6. The interconnected porous network structure ofclaim 1, wherein said nanoparticles are selected from the groupconsisting of silica, alumina, beryllia, noble metal oxides, platinumgroup metal oxides, titania, zirconia, hafnia, molybdenum oxides,tungsten oxides, rhenium oxides, tantalum oxide, niobium oxide, chromiumoxides, scandium, yttrium, lanthanum, ceria, and rare earth oxides,thorium and uranium oxides and combinations thereof.
 7. Theinterconnected porous network structure of claim 1, wherein saidnanoparticles are grown in size up to and including to form a continuousshell residing predominantly at the interface between said network ofsolid material and said network of pores.
 8. The interconnected porousnetwork structure of claim 1, wherein said nanoparticles are selectedform the group consisting of metal nanoparticles, semiconductornanoparticles, metal oxide nanoparticles, mixed metal oxidenanoparticles, metal sulfide nanoparticles, metal chalcogenidenanoparticles, metal nitride nanoparticles, metal pnictide nanoparticlesand combinations thereof; and wherein the solid material is selectedfrom the group consisting of silica, titania, alumina, zirconia, hafnia,inorganic sol-gel derived oxides, polymers, random copolymers, blockcopolymers, branched polymers, star polymers, dendritic polymers,supramolecular polymers, metals and combinations thereof.